Size and longevity of seed banks in Antarctica and the influence of ultraviolet-B radiation on survivorship, growth and pigment concentrations of Colobanthus quitensis seedlings

Populations of Colobanthus quitensis and Deschampsia antarctica, the only t wo vascular plant species native to Antarctica, are increasing. We performe d a seed bank assay to determine the persistence of seeds from intact veget ation/soil cores collected near Palmer Station on the west coast of the Ant arctic Peninsula. Vegetation/soil cores were cold stratified at 3 degreesC for >4 years. Subsequent seed bank densities, estimated from seedlings germ inated, averaged 847 and 5645 seedlings m(-2) for C. quitensis and D. antar ctica. respectively. We also conducted germination trials on C. quitensis s eeds collected at our field site and stored for either 120 days or >4 years at 3 degreesC. Germination rates ranged from 6% after 120 days of cold sto rage to 38% after >4 years of cold storage. These findings show that previo us estimates of seed bank densities and germination rates in these species. based on short-term laboratory stratification experiments. may underestima te there found in the field. Stratospheric ozone depletion has lead to incr eases in ultraviolet-B radiation (UV-B, 280-320 nm) along the Antarctic Pen insula during the austral spring. In a separate experiment we manipulated l evels of biologically effective UV-B (UV-B-BE), over current-year C. quiten sis seedlings near Palmer Station on the west coast of the Antarctic Penins ula by placing frames over them that either held filters that absorbed most UV-B-BE ('reduced UV-B-BE'). transmitted most UV-B-BE ('near-ambient UV-B- BE') or had no filters ('ambient UV-B-BE). We monitored seedling survivorsh ip over the course of the growing season (January-March) and growth acid pi gment concentrations at the end of the season. There were no UV-B,, treatme nt effects on seedling survivorship oc er the course of the season and over winter survivorship averaged 12%. However, seedlings growing under near-amb ient and ambient UV-B-BE had 25 and 48% smaller total leaf areas, 7 and 16% fewer leaves and 65 and 82% fewer branches, respectively, than those growi ng under reduced UV-B-BE. In addition, concentrations of methanol-soluble U V-B-absorbing compounds were 26% higher and concentrations of chlorophyll b were 26% lower in leaves of seedlings growing under ambient UV-B-BE compar ed with those under reduced UV-B-BE. (C) 2001 Elsevier Science B.V. All rig hts reserved.